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Rice-Root Nematode, Hirschmaniella oryzae, Infecting Rice Selections and Weed Genotypes.

Byline: Safdar A. Anwar, M. V. McKenry and S. I. Yasin

Abstract

The occurrence of Hirschmaniella oryzae in roots of 11 rice, Oryza sativa, selections and 10 weed genotypes belonging to 7 families was recorded during 2006-07. Nematode density in composite root samples was determined by a Modified Sieving-Baermann Funnel technique. Root population levels of the nematode varied among rice selections and weeds. Ten rice cultivars including Super Basmati, Basmati-198, Basmati-2000, Basmati-370, Basmati-385, KSK-133, KSK-201, KSK-282, IR-6, and IR-9 exhibited nematode population levels in excess of the damage threshold level (5-30 nematodes per g of root). Only Basmati Pak supported nematode populations below the damage threshold level. The Basmati selections supported varying levels of nematodes with Basmati -370, Basmati-385 and Super Basmati supporting significantly greater nematode populations than Basmati 370, Basmati 198, Basmati Pak and Basmati 2000 selections. Two IR selections supported similar numbers of nematodes but fewer than KSK selections.

Six weed sp cies including Echinochloa colona, E. glabrescens (poaceae), Chenopodium album (chenopodiaceae), Cyperus difformis, Rumex dentatus (polygonaceae), and Scripus maritimus (cyperaceae), supported nematodes at population levels similar to that recovered from rice roots.

Four other weed species including Coronopus didymus (brassicaceae) Marsilea minuta (marsileaceae), Paspalum distichum (poaceae), and Sphenoclea zeylanica (campanulaceae) were consistently infected by the nematode but at population levels reduced from those found in rice roots. This study indicates that rice-root nematode is able to infect all commercially grown cultivars and weeds common to Pakistani rice fields. These results further demonstrate that weed hosts act as a reservoir for over-wintering H. oryzae.

Key words: Rice cultivars, rice-root nematode, Hirschmaniella oryzae, weed genotypes.

INTRODUCTION

Rice (Oryza sativa L. Family : Gramineae) is the most important food grain crop in Pakistan and is commonly planted in all agro-ecological areas suited for rice production. Rice is a major rainy season crop and the best quality rice is grown in central Punjab. Despite an increasing trend to use more inputs and adopt improved production technologies, yield is 22% less than that found in other developed countries (FAO, 2008; Regmi et al., 2002). Various factors are responsible for reduced yield including lack of irrigation as well as outbreaks of specific insects, pests, and diseases (Pimente et al., 1984). Among the diseases, rice blast, bacterial blight, and sheath blight are important diseases of rice (Dahal et al., 1990). Nematodes feed on roots and reduce their potential for uptake of water and nutrients (Mojtahedi and Lownsbery, 1975), but this hidden pest and its associated damage are generally hidden from the growers.

More than 150 genera of plant parasitic nematodes have been reported to be associated with rice production throughout the world (Fortuner and Merny, 1979). Rice-root nematode (Hisrschmanniella spp.) and root-knot nematode (Meloidogyne spp.) are the most important pests of rice (Fortuner and Merny, 1979). The extent of damage by these nematodes in rice depends upon the location, environment, varieties, soils, and other cultural practices associated with rice production.

Numerous weed species are common in rice fields and can reduce yield and quality of rice by competing for light, nutrients and space. In addition, their seeds can be a contaminants of harvested grain. Although competition is the most important effect weeds have on crop production; they are also alternative hosts for plant-parasitic nematodes and have long been recognized for their ability to maintain nematode populations. Weeds can serve as a reservoir for many nematode species (Belair and

Benoit, 1996; Castillo et al., 2008; Davidson and Townshend, 1967; Tedford and Fortnum, 1988; Venkatesh et al., 2000). Numerous species of grass and broadleaf weeds can be found infesting rice fields of Pakistan (Anwar et al., 2008, 2009).

The objective of this study was to determine the relative population levels of rice-root nematode, H. oryzae, in roots of eleven rice, O. sativa, selections and ten weeds commonly associated with rice grown in the Punjab.

MATERIALS AND METHODS

Nematode sampling in each of our field experiments was done according to the methods of Barker (1985). Five samples consisting of roots and soil were collected from each plot of eleven rice selections at panicle stage planted at the farm of Rice research Institute, Kala Shah Kaku, Sheikpura. The selections included Super Basmati, Basmati-198, Basmati-2000, Basmati-370, Basmati-385, Basmati Pak, KSK-133, KSK-201, KSK-282, IR-6, and IR-9. Five plants of each weed species from each plot were randomly sampled. Each sample was comprised of the aerial part of the plant and the corresponding roots with adhering soil collected between the 5 and 30-cm depth. After identification of the plant to species level (Fournet and Flore, 1978; Fournet and Hammerton, 1991) all root samples were carefully washed under tap water to remove adhering soil particles and entangled foreign or weed fibrous roots. The soil suspension was passed through a 60-mesh sieve nested over a 325-mesh sieve.

The material over the 325-mesh was trans erred onto funnels and extracted by Modified Sieving- Baermann Funnel technique (McKenry and Roberts, 1985).

The collected rice root samples were washed thoroughly, cut into 1-5 cm lengths and the nematodes extracted from a fresh rice root composite sub-sample of 20 g by placing them in a mist-chamber for 5 days (McKenry and Roberts, 1985). A weed root sub-sample of 3 g per plant was processed as above.

Data analysis

Data were subjected to analysis of variance using SAS (SAS Institute, Cary NC). Significant differences in means of nematode reproduction were separated using Duncan's Multiple Range Test at (P = 0.05).

Table I.- Rice-root nematode, Hirschmaniella oryzae

Table I.-###Rice-root###nematode,###Hirschmaniella###oryzae

###associated with 11 rice selections.###

###Nematode population in 100 ml3 soil

Rice selections###and root g-1###

###Soil###Root###

Basmati 370###23c###32ab###

Basmati 198###15d###22d###

Basmati Pak###12d###02e###

Basmati 385###35a###32ab###

Super Basmati###26bc###33ab###

Basmati 2000###23c###26cd###

IR-6###26bc###26cd###

IR-9###27bc###29bc###

KSK 282###31ab###34ab###

KSK 133###28b###30abc###

KSK 201###30ab###35a###

*Means within a column followed by the same letter are not significantly different according to Duncan's Multiple Range Test at P = 0.05.

RESULTS

Population levels of H. oryzae

Nematode root populations varied among rice selections (Table I). A significantly low root population level was detected on rice selection Basmati Pak only. Meanwhile, soil population levels were lowest on Basmati 198 and Basmati-Pak selections. Rice selections including, Basmati-385, Super Basmati, KSK -282, KSK -133, and KSK-201 supported high root nematode populations, while Basmati-385, and KAK- 201 also had high soil population levels. Three rice selections namely Basmati 2000, IR-6, and IR-9 had intermediate root and soil populations. Nine rice selections including Super Basmati, Basmati-2000, Basmati-370, Basmati-385, KSK- 133, KSK- 201, KSK-282, IR -6, and IR-9 exhibited nematode population levels in excess of the damage threshold level (5- 30 nematodes per g of root) (Ying et al., 1996; Zin et al., 2010). Two selections including Basmati-198 and Basmati Pak supported nematode populations below the damage threshold level.

The Basmati selections supported varying levels of nematodes. Basmati-370, Basm ti-385, and Super Basmati supported significantly greater nematode populations than three other Basmati selections.

Two IR selections supported the same number of nematodes but significantly fewer than KSK selections.

Weeds infesting rice crops

Ten weed species belonging to 9 genera and 7 families were found infesting rice fields. Among these ten weed genotypes, there were six annual weed species (Chenopodium album, Coronopus didymus, Cyperus difformis, Echinochloa colona, E. glabrescens, Sphenoclea zeylanica) and four perennial species (Marsilea minuta, Paspalum distichum, Rumex dentatus, Scripus maritimus) (Table II).

Hirschmaniella oryzae in association with weeds

All the weed genotypes supported varying levels of nematodes during rice cropping season as well as during the off-season (Table III). Six weed genotypes including C. album, C. difformi, E. colona, E. glabrescens, R. dentatus, and S. zeylanica sampled from rice fields exhibited high soil nematode populations, while soil of four other genotypes comprising of C. didymus, M. minuta, P. distichum and S. maritimus exhibited reduced nematode populations in soil.

The nematode populations from roots were highest (P= 0.05) from E. glabrescens, intermediate from C. difformi and E. colona, and lowest from roots of the other seven weed genotypes.

Weed genotypes C. difformis and E. glabrescens had similar root nematode populations during off and on season. Weed genotype P. distichum supported the lowest nematode population during both harvests. Nematode populations found in rhizosphere soil were also variable among weed genotypes. Two weed genotypes M. minuta and P. distichum supported lowest soil nematode populations during both sampling seasons. Only one weed genotype

E. glabrescens exhibited low soil nematode populations during off-season. Six other weed species including C. album, C. didymus, E. colona, P distichum, R. dentatus and S. maritimus supported high soil nematode populations during both seasons.

DISCUSSION

The primary objectives of this study were to etermine the host status of H. oryzae in association with rice selections and weed genotypes in Punjab rice production (See Table I). Eleven rice cultivars and ten weed genotypes were evaluated in several rice plantings. The results showed statistical differences in H. oryzae population development in association with both rice and weed genotypes. These differences among nematode population levels were due to variation in the genetic make-up of genotypes (Brian et al., 2010). Differences in host status may also have been due to variations in farm practices, location, environment, soils and other cultural practices in rice production (Prasad, 1987). These findings are similar to results obtained by Pokharel, 1991.

This study has demonstrated that population levels of rice-root nematode, H. oryzae exceeded accepted damage threshold levels on roots of ten out of eleven rice selections (Ying et al., 1996; Zin et al., 2010). Data suggest that rice-root nematode might be the most important damaging soil pest in rice growing areas of the Punjab. The occurrence of this nematode has been reported from rice producing regions throughout the world (Bridge et al., 2005).

The eleven rice selections we studied were derived from three sources including Basmati, IR and KSK. Six Basmati selections demonstrated high variability to infection by rice-root nematode populations. Abundance of nematodes on Basmati 385, intermediate levels on Super Basmati and Basmati 370 but low levels on two others, Basmati Pak and Basmati 198, suggests these selections differ in their level of resistance and this source warrants screening for an improved source of nematode resistance. Meanwhile, IR and KSK selections exhibited statistically similar levels of infestation within their respective group and may prove less worthy as a source for improved resistance.

In this study, 10 weed species hosted H. oryzae and all life stages could be found in the cortical tissue of the roots (Table III). The presence of abundant rice- root nematode in roots of weed genotypes during the off-season could provide a useful bio-indicator of the level of H. oryzae in fallow fields prior to rice replanting. Nematode and weed populations interact in numerous ways and the

376 S.A. ANWAR ET AL.

Table II.- Listing of 10 common weeds assessed for their nematode host status

Weed genotypes###Common name###Family###Life span###

Chenopodium album###Lamb's-quarters###Chenopdiaceae###Annual###

Coronopus didymus###Swine cress###Brassicaceae###Annual###

Cyperus difformis###Flate sedge###Cyperaceae###Annual###

Echinochloa colona###Jungle rice###Poaceae###Annual###

E. glabrescens###Orange torch###Poaceae###Annual###

Marsilea minuta###Water clover###Marsileaceae###Perennial###

Paspalum distichum###Knot grass###Poaceae###Perennial###

Rumex dentatus###Curled dock, Sour dock###Polygonaceae###Perennial###

Scripus maritimus###Bulrush###Cyperaceae###Perennial

Sphenoclea zeylanica###chickenspike###Sphenocleaceae###Annual

Bulrush###

Sphenoclea zeylanica###

Table III.-###Population levels of rice-root nematode, Hirschmaniella oryzae, on weeds.###

Weed genotypes###Nematode population during###

###Rice growing season###Rice land, off-season###

###Soil per 100 ml3###Root g-1###Soil per 100 ml3###Root g-1###

Chenopodium album###61bc###12bc###71ab###15ab###

Coronopus didymus###55de###11bc###65ab###17ab###

Cyperus difformis###65ab###13b###60b###13b###

Echinochloa colona###68a###14b###69ab###15ab###

E. glabrescens###60c###19a###77a###18a###

Marsilea minuta###45f###9bc###44c###8c###

Paspalum distichum###39g###7c###43c###9c###

Rumex dentatus###67a###12bc###62ab###17ab###

Scripus maritimus###53e###11bc###58b###15ab###

Sphenoclea zeylanica###59c###13b###69ab###17ab###

*Means within a column followed by the same letter are not significantly different according to Duncan's Multiple Range Test at P = 0.05. persistence of weeds growing among rice roots or between two successive rice crops is an important source of nematode survival and infestation. This study suggests that weeds can be an important reservoir of rice-root nematode, H. oryzae (Table III). Four annual weeds including two Echinochloa species (jungle rice, orange torch), one Paspalum species (knot grass), one Cyperus species (flat sedge) are the most widespread and aggressive weeds of rice. It is also interesting to note that plants from the Cyperaceae, Poaceae, Sphenocleaceae families were hosts of H. oryzae. They are also a good host of rice-root nematode (Babatola, 2006). This suggests that rice cultivation, which favors the re-growth of these weeds may favor survival of H. oryzae and help to explain the re-infestation of rice after a fallow period.

Conversely, the good weed host for nematodes will also be dama ed along with the cash crop resulting in less competition. Gonzalez Ponce et al. (1995) showed that tomatoes infected with M. incognita were less competitive with black nightshade (Solnum nigrum), a good host for root-knot nematode. The growth of relatively poor weed hosts to nematodes is likely to be unaffected leading to more competition with crop plants. Starr (1998) found that nematode parasitism reduces cotton growth but the growth of weeds being poor host is not affected. Nematode parasitism of a crop has been shown to increase the effects of competition from weeds when soybean ( Glycines max) growth was reduced by soybean cyst nematode (Heterodera glycines) damage (Alston et al., 1991).

Our findings suggest that weed plants provide a means of survival for nematode populations which may contribute to the maintenance, reinfestation, multiplication and spread of H. oryzae within a field, and thus increase the potential for crops to be damaged by nematode attacks (Castillo et al., 2008). Infested fields act as an important reservoir of nematodes and may aid in the dissemination of nematodes within or among crops by many agricultural operations like irrigation water (Orr and Newton, 1971) that can reduce the beneficial effects of the nematode resistant crops. We had also demonstrated that rice selections differ in their level of resistance and this source warrants screening for an improved source of nematode resistance. Our findings further suggest that rice selection Basmati-Pak offers resistance over other selections, which is a better choice for grower to plant in the nematode infested fields.

ACKNOWLEDGEMENTS

This research was made possible thanks to Higher Education Commission, Islamabad, Pakistan, for providing funds through project # 455.

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0030-9923/2011/0002-0373 $ 8.00/0 Copyright 2011 Zoological Society of Pakistan.

Department of Plant Pathology, University of Agriculture, Faisalabad, Pakistan. 2Department of Nematology, University of California, Riverside, CA 92521. 3Rice Research Institute, Kala-Shah-Kaku, Pakistan.
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